While the theoretical basis and effectiveness of print-based, tailored smoking cessation interventions have been examined in numerous studies, very little research has been conducted on the effectiveness of computer-tailored smoking cessation interventions delivered via the World Wide Web. Further, researchers in public health communications have little knowledge about the active ingredients of tailoring, the components that contribute to its effectiveness. This project proposes to examine the significance of a potential active ingredient: depth of tailoring. Depth of tailoring refers to the level of detail of tailoring and the interactions among theory-based tailoring constructs. A low-depth intervention may generate thousands of message combinations, while a high-depth program may generate billions of variations. High-depth interventions can create extensively tailored cessation messages, but do they result in better outcomes? Is it worth the time and energy to develop such comprehensive interventions? In a randomized 1x3 factorial design among 3,000 smokers, the study will compare the effectiveness of low versus medium-versus high-depth of tailoring in achieving 12-month smoking cessation rates. The study will also examine the impact of tailoring depth on smoking reduction, stage of change, and baseline characteristics such as gender, income, and education. The study will collaborate with Henry Ford Health System of Detroit to recruit participants and to implement the web-based interventions. As the number of web-based cessation programs increases and more people turn to the World Wide Web for health information, a highly interactive medium which is capable of reaching large numbers of smokers at any time and at little cost, we believe the field is posed to examine specific aspects of tailoring that influence its effectiveness in web-based smoking cessation interventions. Such research may provide understanding of why some tailored interventions positively influence cessation and insight into how to create other highly effective tailored interventions.